It is well known that yarn bundles of continuous fiber filaments lack cohesion between the individual filaments. During processing of the yarn bundles into textile products this lack of cohesiveness causes individual filaments to catch or snare on the processing equipment, thus leading to filament breakages and irregularities in the textiles. This problem is especially pervasive during knitting of the yarn bundles into a fabric. Non-cohesiveness of the yarn bundles also leads to excessive spreading of the filaments which increases the frictional contact between the processing equipment and the individual filaments resulting in abrasion and breakage.
One method for providing cohesion between the filaments is the use of what is known variously as entangling, mingling, commingling or interlacing. The term "entangling" will be used herein for convenience but the other equivalent terms could just as easily be substituted therefor.
Entangling is a process which forms a series of intermittent sections along the length of the yarn wherein the individual filaments are tightly entangled with each other. These entangled sections are known variously as entanglements, nips, nodes or knots and are separated from each other by lengths of filaments wherein the individual filaments are relatively parallel to each other. The entanglements act to prevent the individual filaments from spreading and splaying during processing of the yarn into a fabric, thereby maintaining a cohesive yarn bundle.
Conventional entangled yarn is formed by an apparatus referred to as an air jet. Numerous different air jet embodiments have been envisioned (see, e.g., U.S. Pat. No. 4,729,151 which includes an extensive discussion of the development of air jets). Indeed, there are many types of jets currently utilized such as closed jets, forwarding jets and slotted jets. All air jets, however, generally include a yarn chamber extending the length of the jet body which accomodates various yarn deniers and an air orifice which is used to direct an air flow into the yarn chamber to cause the entangling of the filaments. An air jet is presumed to form an entangled yarn as follows:
Within the air jet the loose bundle of continuous multifilament yarn is subjected to a turbulent gas stream contacting the yarn at right angles to its axis. The gas stream spreads open the filaments and, within the immediate vicinity of the spread open section, forms a plurality of vortexes which cause the filaments to become entangled. The alternating entanglement nodes and non-entangled sections are formed as the yarn travels through the chamber.
The prior art discloses entangled yarns which are produced at a high filament feed rate. For example, U.S. Pat. No. 4,535,516 discloses an air jet which is said to produce at high filament feed rates a multifilament yarn having at least 20 entanglements/meter. U.S. Pat. No. 4,237,187 discloses a process for producing an entangled multifilament polyamide yarn at windup speeds of from 3500 to 6000 meters/minute. Neither one of these patents, however, describe a yarn having sufficient entanglement strength.
Although attempts have been made to objectively characterize the relationships between the various parameters that effect entangling, the art of entangling remains highly unpredictable as noted, for example, by Demir and Acar in their "Insight Into the Mingling Process" paper presented at the Textile Institute World Conference, Oct. 1989, and published by the Textile Institute in Textiles: Fashioning the Future. One attempt to characterize a yarn in terms of the degree of entanglement is found in U.S. Pat. No. 4,118,921. This patent describes an entangled yarn having an entanglement pin count of 3 to 50 mm and the fibers having a number average fiber length of 18 to 60 cm with a distribution of fiber lengths such that at least 5 percent of the fibers are no longer than 12.7 cm, 50 to 93.5 percent are longer than 12.7 cm but no longer than 76 cm, and at least 1.5 percent are longer than 76 cm.
Prior efforts have been directed to the development of myriad air jets each serving a unique function in that they are designed to impart special limited characteristics to the entangled yarn. The emphasis has been placed upon achieving a certain distribution of entanglements, measured primarily in terms of entanglements per meter. There exists a need, however, for an entangled yarn with improved entanglement strength.